Dual voltage charging systems are known for maintaining two series connected batteries at equal voltages for supplying power to a pair of variable loads. Such dual voltage charging systems have included a battery equalization circuit with two independent sensing networks each requiring an individual reference voltage. This type of equalization circuit does not provide automatic tracking of the battery voltages. Further, because of the duplicate sensing networks and the need for dual calibration, this type of circuit is costly and inefficient. This type of circuit is also susceptible to temperature drift.
Other battery equalization circuits for dual voltage charging systems have included a voltage divider circuit coupled to the batteries. The voltage divider circuit provides a reference voltage that is equal to half the total voltage across the batteries. A regulated D.C. to D.C. converter has its output connected across one of the batteries for charging that battery to a level indicated by the reference voltage. The voltage divider of this battery equalization circuit must either be calibrated or include expensive precision resistors in order to set a precise reference voltage for maintaining a balance between the voltages provided by the batteries. Further, the resistors in the voltage divider must have matched temperature coefficients to maintain the balance between the battery voltages over a range of temperatures.